120 MR. HENFREY ON THE DEVELOPMENT 



layer lining the wall, others lying in the more internal parts of the cavity (fig. 13). In 

 some cases the chlorophyll globules are so closely packed, in isolated cells, as to acquire a 

 parenchymatous form from mutual pressure (fig. 14). These chlorophyll globules present 

 in a high degree those characters found in the same structures in all the higher Crypto- 

 gamous plants, — characters which appear to warrant Nageli's view that the chlorophyll 

 is contained in a membranous vesicle, and that these vesicles are increased in number by 

 a process of subdivision like that of cells. I have met with appearances which I cannot 

 explain in any other way, but shall be content with a mere indication here, to avoid 

 digressing from the immediate subject of this Memoir. I believe that I have seen the 

 enveloping membrane enclosing a green fluid (fig. 15) ; moreover, the development of two 

 or more starch-granules inside those vesicles, so as gradually to displace the chlorophyll ; 

 but as the vesicles are only about -g^ooth or 10i o 00 th of an inch in diameter, much eareful 

 examination is requisite before a safe decision can be arrived at. 



In some cells I have seen a small colourless and formless accumulation of mucilage 

 upon the side wall, among the chlorophyll globules. It is possible that this may have 

 been a nucleus. I also found a large clear and circular vesicle in one of the cells of an 

 old barren prothallium ; this had all the appearance of a nucleus, excepting that it was so 

 exceedingly transparent. In the vegetative cells generally I saw no trace of nuclei. 



The cells of the older posterior part of the prothallium contain but little chlorophyll, 

 and like the root-filaments, are filled with colourless, slightly granular mucilaginous fluid ; 

 and they often appear stained with brown patches, arising from the partial decay of the 

 walls. In all cases the death of the cell-membrane is followed by a brown colouring of 

 the dead part. 



Such is the normal history of a prothallmm, so far as its vegetation is concerned (for 

 the reproductive structures, left out of view in the preceding description, are in part deve- 

 loped at a very early period). If the regular development of a leafy stem takes place, a 

 term is naturally set to the existence of the prothallium, which quickly decays away as 

 the young stem grows up. But if the prothallium remains barren, if none of the arche- 

 gonia become fertilized, its vegetative existence may be continued for a long time. The 

 lateral lobes grow much larger, their borders become curved and sinuous, or variously 

 convoluted ; new lobes sometimes grow out from the cushion-like thickening in the 

 middle ; and, finally, individual cells of the margin may grow out and repeat the mode of 

 development exhibited by the spore-cell in the original germination, so as to produce new 

 prothallia (by a process of budding), which become detached from the parent (fig. 12). 

 The progeny of • proliferous ■ prothallia exhibit antheridia, but I have never seen arche- 

 ffonia upon them. In other respects they are exact repetitions of the parent structure. 



II. The Antheridia. 

 The organs to which this name is applied are produced in much greater abundance than 

 those which are indicated by the term archegoniwm, and they present themselves through- 

 out almost every stage of the growth of the prothallium, in some cases from the time 

 when it consists of a mere collection of some dozen cells, in others not until the cordate 

 form has become evident, until the latest period ; so that since they run through their 



